Magnetic resonance imaging systems rely on the tendency of atomic nuclei possessing magnetic moments to align their spins with an external magnetic field. Because only nuclei with odd numbers of nucleons have a magnetic moment, only those nuclei can be detected and imaged using magnetic resonance. At present, hydrogen with one nucleon, a proton, in its nucleus is the element of choice for diagnostic tissue imaging.
Magnetic resonance imaging data obtained using non-metabolically derived hydrogen, although useful in providing information on tissue perfusion (blood flow to that tissue) and structure, are of limited use in detecting the metabolism of those tissues. Visualization of tissue metabolism using magnetic resonance imaging can be obtained by imaging H.sub.2 O formed during aerobic metabolism.
Under aerobic conditions, H.sub.2 O is formed as a byproduct of oxygen consumption. The metabolic formation of H.sub.2 O can be detected using isotopes of oxygen. The most common isotope of oxygen, oxygen-16, has an even number of nucleons and, thus, cannot be imaged in a magnetic imaging system. Another isotope of oxygen, oxygen-15, is unstable with a short half life (radioactive) and its use would expose a subject to potentially harmful radiation.
The oxygen isotope, oxygen-17 (.sup.17 O.sub.2, is stable, has an odd nucleon number and is suitable for use in magnetic resonance imaging. Further, because .sup.17 O.sub.2 can be detected by a proton magnetic resonance imaging in the form of H.sub.2.sup.17 O, the use of .sup.17 O.sub.2 provides data on the metabolic state of imaged tissues.
A magnetic resonance imaging process using .sup.17 O.sub.2 has been previously reported. In accordance with that process, .sup.17 O.sub.2 is administered intravenously in an artificial blood composition comprising perfluorohydrocarbons as the oxygen carrier. See U.S. Pat. No. 4,996,041, the disclosure of which is incorporated herein by reference. Because of the limited oxygen-carrying capacity of perfluorohydrocarbons, that process requires loading the patient with large volumes of the artificial blood composition. Further, the effects of artificial blood compositions per se on tissue metabolism are not yet known.
PCT Patent Publication No. WO 91/07990 reports the use of an inhalant gas containing .sup.17 O.sub.2 as a nuclear magnetic imaging agent. That process requires large volumes of expensive .sup.17 O.sub.2 gas and is limited in its use to subjects having normal respiratory function. Large volumes of inhalant gas are needed in that process because only a small portion of the inhaled gas comes in contact with the blood.
Oxygen absorption into the blood can occur through from the peritoneal cavity. Wilks, S., J. Appl. Physics, 14:311 (1939) and Van Liew et al., Microvascular Research, 1:257 (1969). Not only does the peritoneal cavity offer a large surface area for absorption (equivalent to that of skin), but also the membrane surfaces in the peritoneal cavity (the peritoneum and the omentum) are readily supplied with capillary vessels that provide ready access to the blood. Indeed, anoxic animals (animals with a deficiency in blood oxygen tension) can be successfully oxygenated with oxygen delivered into the peritoneal cavity. Bilge et al., Biomaterials, Artificial Cells, Artificial Organs, 17(4):413 (1989).